nordic::gattc_uuid128_acquire() will not work for multiple GATTC connections

[natersoz]

The implementation for discovering 128-bit UUIDs using the Nordic softdevice will work find
for single connection GATT clients. However, for multiple GATTC clients the stored struct uuid128_read_pending_t instance will conflict.

The struct uuid128_read_pending_t instance needs to be included somewhere in the ble::gattc::connectable hierarchy so that there is one instance per connection.

See ble/nordic_ble_gattc_event_observable.cc gattc_uuid128_acquire() comments.

[natersoz]

This issue needs a second part:
The hack is also hard coded to primary service discovery when it could be any part of service discovery.